JP4243912B2 - Method for recovering crystals from slurry - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for recovering crystals from a slurry containing crystals, and is used in various organic chemical product manufacturing processes, such as a process for producing terephthalic acid by liquid phase oxidation of paraxylene.
[0002]
[Prior art]
When terephthalic acid is produced by liquid phase oxidation of para-xylene, the terephthalic acid produced is precipitated as crystals in the mother liquor, producing a slurry containing terephthalic acid crystals. When crystals are recovered from this slurry, crude terephthalic acid is obtained. Moreover, when the obtained crude terephthalic acid is dissolved and terephthalic acid is precipitated through purification steps such as oxidation treatment and reduction treatment, a slurry containing crystals is obtained.
In any of the above cases, as a method of recovering crystals from the slurry, a method of performing suction filtration, washing, suction filtration, and peeling in one operation with a rotary vacuum filter (hereinafter referred to as RVF) is often employed.
[0003]
[Problems to be solved by the invention]
The RVF sequentially performs suction filtration, washing, suction filtration, and peeling while rotating a cylindrical filter medium. However, in this method, since the filter medium is clogged by continuing the operation, it is difficult to operate for a long time.
An object of the present invention is to propose a method capable of continuously recovering crystals for a long period of time without causing clogging of a filter medium when recovering crystals from a slurry using RVF.
[0004]
[Means for Solving the Problems]
As a result of intensive studies on the RVF having the above-mentioned problems, the inventors have supplied the solvent component vapor to the blowing gas used for peeling the cake in the RVF peeling process, thereby removing the cake from the filter medium. As a result, the present inventors have found that the RVF can be operated continuously for a long period of time.
[0005]
That is, the present invention peels cakes in a method in which slurry comprising crystals and a solvent is supplied to a rotary vacuum filter, and a cylindrical filter medium is rotated to perform suction filtration, washing, suction filtration, and cake peeling continuously. A method for recovering crystals from a slurry, characterized in that a solvent component vapor is supplied to a blowing gas for the purpose.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of an RVF, and FIG. 2 is a system diagram of a crystal recovery method showing a preferred embodiment of the present invention.
In the sectional view of FIG. 1, a horizontal cylindrical filter medium 3 is rotatably installed in a casing 2 of RVF1. The lower part of the filter medium 3 is a filtration zone 5 immersed in the slurry 4 stored in the lower part of the casing 2, and a suction part 8 for sucking the filtrate 6 and the blowing gas 7 is formed inside thereof.
[0007]
A cleaning liquid pipe 10 for cleaning the cake 9 is provided on the upper part of the filter medium 3, and the filter medium 3 has a cleaning area 11 and a drainage area 12 corresponding to the cleaning liquid pipe 10. A liquid portion 13 is formed.
Inside the filter medium 3, there are provided a blow part 14 and a seal part 15 for peeling the cake 9, and the filter medium 3 has a peel zone 16 corresponding to the blow part 14 and non-condensable such as nitrogen gas. A blowing gas supply pipe 17 for supplying a blowing gas in which solvent vapor is mixed with gas is installed.
The slurry to be processed in RVF1 is supplied from a slurry supply unit 18, and a dam 19 is installed to hold the slurry liquid level. Slurry overflowing from the dam is discharged from the slurry circulating section 20, and the cake is discharged from the cake outlet 21.
[0008]
In the system diagram of FIG. 2, the slurry to be treated is supplied from the slurry storage tank 22 to the slurry supply unit 18 of the RVF 1 by the pump 23, discharged from the slurry circulation unit 20, and circulated. The cleaning liquid in the liquid collection unit 13 is discharged out of the system by the pump 24.
The filtrate and blowing gas from the suction unit 8 in FIG. 1 are sent to the filtrate tank 25, and the filtrate is discharged by the pump. A cooler 27 is installed in the upper part of the filtrate tank 25, and the cooled gas separates the mist with a mist separator 28 and is discharged by a vacuum pump 29. The discharge of the vacuum pump 29 includes a sealing liquid separator 30 and a mist separator 36, and the gas discharged from the vacuum pump 29 is used as an RVF blowing gas.
The cake peeled off at RVF1 is taken out from the cake take-out section 21 shown in FIG. 1 through the shutter 33 and the shutter 34, dried by the dryer 35, and collected as crystals (product) from the product take-out port 36.
[0009]
In the crystal recovery method, the slurry stored in the slurry storage tank 22 is supplied to the bottom of the RVF1 by the pump 23, and the filter medium 3 is rotated, and suction filtration, washing, suction filtration, and peeling (blowing) are sequentially performed. This will be specifically described below.
As a result of the vacuum pump 29 being operated, the inside of the rotating drum becomes negative pressure through the suction part 8, and as a result, the slurry supplied to the bottom of the RVF 1 is filtered by the rotating filter medium 3, and the crystals in the slurry 4 are captured by the filter medium 3. It becomes cake 9 and rises. A part of the slurry 4 overflows the dam 19 and circulates from the slurry circulation part 20 to the slurry storage tank 22.
The cake 9 is washed in the washing area 11 by the washing liquid sprayed from the washing liquid pipe 10, and the washing liquid is removed in the liquid removal area 12 and descends. In the peeling area 16, the blowing gas is supplied to the blowing gas supply pipe 17 and sprayed from the blowing unit 14 to peel the cake 9. The filter medium 3 from which the cake 9 has been peeled further descends and reaches the filtration zone 5 again.
The filtrate 6 and the blowing gas 7 sucked from the suction part 8 enter the filtrate tank 25, and the filtrate 6 is discharged out of the system by the pump 26.
The cake 9 peeled in the peeling area 16 is taken out from the cake take-out section 21 via the shutter 33 and the shutter 34, dried by the dryer 35, and collected as crystals (product) from the product take-out port 36.
[0010]
The eye of the present invention is to install a solvent vapor supply line 32 to the blowing gas exiting the mist separator 31 and supply solvent component vapor. For example, when the mother liquor of the slurry 4 is water, the solvent component vapor is naturally water vapor. Further, when the mother liquor of the slurry 4 is hydrous acetic acid, hydrous acetic acid vapor having a configuration close to the mother liquor composition is optimal, but water vapor or acetic acid vapor may be used.
In the case of a normal terephthalic acid production apparatus, one or more crystallization tanks are installed upstream of the slurry storage tank 22. Since the slurry temperature is lowered by flash evaporation of the solvent in the crystallization tank, it is convenient to supply the vapor generated there from the solvent vapor supply line 32.
[0011]
By supplying the solvent component vapor from the solvent component vapor supply line 32, the filter medium is not clogged as a result, and it has become possible to operate continuously for a long period of time. The reason is still unclear, but is presumed to be due to several complex cures.
The first estimation reason was that the capacity of the blowing gas could be increased by supplying the solvent component vapor. As a result, it can be expected that the crystal is completely peeled in the peeling region 16. After the solvent component vapor supplied from the solvent component vapor supply line 32 is used as a blowing gas, it is discharged from the suction unit 8 to the filtrate tank 25. Even if the capacity increases, it is advantageous because it hardly affects the amount of processing gas in the vacuum pump 29.
The second estimation reason was that the wetness of the blowing gas increased by supplying the solvent component vapor. As a result, it can be expected to suppress a decrease in the crystals adhering to the filter medium. In addition, it can be expected that a small amount of the solvent component mist present in the blowing gas will eliminate the fine crystals remaining on the filter medium.
The third estimation reason was that the temperature of the blowing gas was increased by supplying the solvent component vapor. More perfect peeling can be expected by increasing the temperature.
As shown in the example, as a result of mixing the vapor of the solvent component with the blowing gas, the moisture in the crystal of the crystal takeout part 21 was reduced. This is an unexpected effect at first.
[0012]
Since the solvent component vapor supplied from the solvent vapor supply line 32 is used as a blowing gas and then discharged from the suction unit 8 to the filtrate tank 25, the volume of the blowing gas is supplied by supplying the solvent component vapor. Even if it increases, there is no influence on the amount of processing gas in the vacuum pump 29.
In addition, although the temperature decreased between mixing the solvent component vapor and reaching the blow section 14, the risk of mist generation was considered, but according to long-term operation experience, no particular problem occurred . By keeping the temperature of the line reaching the RVF, the decrease in the solvent component vapor temperature can be kept small.
[0013]
Although the present invention is suitable for recovering crystals of crude terephthalic acid and purified terephthalic acid as described above, other catalyst components such as isophthalic acid and naphthalenedicarboxylic acid are used at high temperatures and pressures. It can be applied to a step of recovering crystals from a slurry in a process for producing an aromatic carboxylic acid by oxidation with molecular oxygen in a solvent containing.
[0014]
【Example】
Examples of the present invention will be described below. However, the present invention is not limited by these examples.
[0015]
Example 1
A terephthalic acid / hydrous acetic acid slurry (32% by weight of terephthalic acid, temperature 89 ° C.) obtained from a commercial production apparatus for producing crude terephthalic acid by air oxidation in the presence of cobalt, manganese and bromine catalysts, It processed by the method shown in FIG. 1 and FIG. 2, and collect | recovered crude terephthalic acids. Nitrogen gas is used as the blowing gas, and flash vapor (mixed vapor of acetic acid vapor and water vapor) generated in the flash crystallization tank installed upstream of the slurry storage tank 22 is supplied from the solvent vapor supply line 32 to 780 kg / h. did. The time until the filter medium 3 was clogged was 310 hours. Moreover, the drying loss when the cake collected from the cake take-out part 21 was dried at 110 ° C. for 4 hours was 9.8%.
[0016]
Comparative Example 1
In Example 1, the supply of the flash vapor from the solvent vapor supply line 32 was stopped. That is, only nitrogen gas was used as the blowing gas. As a result, the time until clogging was 24 hours. Moreover, the drying loss when the cake collected from the cake take-out part 21 was dried at 110 ° C. for 4 hours was 11.3%.
[0017]
Example 2
An isophthalic acid / hydrous acetic acid slurry (30 wt% isophthalic acid, temperature 85 ° C.) obtained from a commercial production apparatus for producing crude isophthalic acid by air oxidation in the presence of cobalt, manganese and bromine catalysts, It processed by the method shown in FIG. 1 and FIG. 2, and collect | recovered crude isophthalic acids. Nitrogen gas is used as the blow gas, and the flash vapor (mixed vapor of acetic acid vapor and water vapor) generated in the flash crystallization tank installed upstream of the slurry storage tank 22 is supplied from the solvent vapor supply line 32 to 200 kg / h. did. The time until the filter medium 3 was clogged was 230 hours. Further, the loss on drying when the cake collected from the cake take-out part 21 was dried at 110 ° C. for 4 hours was 10.4%.
[0018]
Comparative Example 2
In Example 2, the supply of the flash vapor from the solvent vapor supply line 32 was stopped. That is, only nitrogen gas was used as the blowing gas. As a result, the time until clogging was 18 hours. Moreover, the drying loss when the cake collected from the cake take-out part 21 was dried at 110 ° C. for 4 hours was 12.1%.
[0019]
【The invention's effect】
As is clear from the above examples, according to the present invention, by supplying the solvent component vapor to the blowing gas for peeling the cake, clogging of the filter medium is prevented, and crystals are efficiently produced from the slurry over a long period of time. It can be recovered.
Further, since the solvent component vapor supplied in the present invention is used as a blowing gas for peeling the cake and then discharged from the gas suction unit to the filtrate tank, it is recovered and used as a solvent, and the capacity of the blowing gas Even if it increases, it does not affect the amount of processing gas in the vacuum pump. Furthermore, the quality of the recovered crystal is improved by increasing the capacity of the blowing gas.
The method for recovering crystals from the slurry of the present invention can be applied to many processes such as a process for producing an aromatic carboxylic acid by liquid phase oxidation, and the industrial significance of the present invention is great.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a rotary vacuum filter used in the present invention.
FIG. 2 is a system diagram of a crystal recovery method showing a preferred embodiment of the present invention.
[Explanation of symbols]
1: RVF (rotary vacuum filter)
2: Casing 3: Filter medium 4: Slurry 5: Filtration zone 6: Filtrate 7: Gas 8: Suction unit 9: Cake 10: Washing liquid tube 11: Washing zone 12: Dewatering zone 13: Liquid collecting unit 14: Blow unit 15 : Sealing part 16: Stripping zone 17: Blowing gas supply pipe 18: Slurry supplying part 19: Dam 20: Slurry circulating part 21: Cake takeout part 22: Slurry storage tank 23: Pump 24: Pump 25: Filtrate tank 26: Pump 27: Cooler 28: Mist separator 29: Vacuum pump 30: Sealing separator 31: Mist separator 32: Solvent vapor supply line 33: Shutter 34: Shutter 35: Dryer 36: Product outlet

Claims (4)

Blowing gas used to peel cake in a method in which slurry consisting of crystals and solvent is supplied to a rotary vacuum filter and a cylindrical filter medium is rotated to perform continuous suction filtration, washing, suction filtration, and cake peeling. A method for recovering crystals from a slurry, characterized in that a solvent component vapor is supplied to the slurry. The crystal from the slurry according to claim 1, wherein a chemical reaction is performed under pressure using a solvent, and a flash vapor of a solvent component obtained when the reaction product liquid is decompressed is supplied to a blowing gas for peeling the cake. Collection method. In the process of producing aromatic carboxylic acid by oxidizing aromatic hydrocarbon with molecular oxygen in a solvent containing catalyst components under high temperature and high pressure, the aromatic carboxylic acid is subjected to a crystallization step in which the reaction product is cooled. 2. A slurry comprising a crystal and a solvent is produced, and the solvent component vapor is supplied to a blowing gas for separating the cake when the aromatic carboxylic acid crystal is separated from the slurry using a rotary vacuum filter. Or the crystal | crystallization collection | recovery method from the slurry of Claim 2. In the process of oxidizing para-xylene with molecular oxygen in a solvent containing a catalyst component, water vapor acetic acid is used as the solvent for the oxidation reaction, and flash vapor (mixed vapor of acetic acid vapor and water vapor) obtained when the oxidation reaction solution is depressurized. The method for recovering crystals from the slurry according to claim 3, wherein crystal recovery of crude terephthalic acid is supplied to the blow gas of the rotary vacuum filter.

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